The development of poly(dendrimer)s for advanced processing

A norbornenyl-based homopolymer that has a dendronised iridium(m) complex attached to every monomer unit has been synthesized. The dendronised iridium(m) complex is comprised of three facially arranged 2-phenylpyridyl ligands. Two of the ligands bear first generation biphenyl-based dendrons with 2-ethylhexyloxy surface groups attached and the third ligand is attached to the polymer backbone via a benzyloxy ester. The polymer was formed by ring opening metathesis using the Grubbs III catalyst and was found to have an Alp of 130 kDa by MALDI-TOF mass spectrometry. At a concentration of 25 mg cm(-3) the polymer solution had a viscosity of 1.09 mPa s, which was 34% higher than a solution containing a dendrimer of same weight per volume. The dendrimer had the same core, dendrons, and surface groups but differed from the polymer in that it had dendrons attached to three of the ligands rather than the two of the polymer. The solution photoluminescence quantum yield (PLQY) of the poly(dendrimer) was found to be 57%, indicating that intra-polymer chromophore interactions were not leading to strong quenching of the luminescence. However, in the solid-state the PLQY dropped significantly, indicating that inter-polymer chromophore interactions were significant. The presence of the dendrons allowed the simple blending of the polymer with 4,4'-bis(N-carbazolyl)-2,2'-biphenyl (CBP), and the blended film had a PLQY of 50%. Simple bilayer devices with a blended emissive layer and an electron injection and transport layer had an external quantum efficiency of 6.2% at a brightness of 100 cd m(-2), showing that poly(dendrimer)s are a promising class of OLED material.